But, again, the concept isn’t difficult. Let’s use the city of Joliet as an example. Joliet’s traditional utility for the 60435 area code is Commonwealth Edison. As of late February, its price to compare is 7.195 cents per kilowatt hour (kWh); at this writing, four plans from ChooseEnergy.com featured suppliers with lower rates, including one that’s 18% cheaper and uses all green energy.